Nuclear estrogen receptor in the avian liver: Correlation with biologic response

Abstract

Diethylstilbestrol (DES) administration to cockerels resulted in an elevation (7-fold) in the number of high affinity binding sites measured in isolated liver nuclei by the [ 3H]-estradiol exchange method. Increases were noted within 60 min, reached a maximum by 4 h and by 48 h had returned to control values. Elevation in the quantity of nuclear binding sites was estrogen-specific and 20% of the [ 3H]-estradiol bound could be extracted by 0.4 M KC1. When isolated chromatin was used to evaluate estrogen-receptor interaction, the binding data were similar to those obtained with intact nuclei. To correlate estrogen binding with a specific hepatic response to this hormone, very low density lipoproteins (VLDL) synthesis was measured by immunochemical techniques in liver slices incubated in vitro in the presence of [ 3H]-lysine following a single injection of DES. An increase in immunoprecipitable VLDL in the liver slices was first noted 2 h after estrogen administration, suggesting that nuclear receptor occupancy occurs prior to the earliest detectable stimulation of protein synthesis. To determine whether receptor binding and protein synthesis were temporally separated by estrogen-induced changes in transcription. RNA polymerase activities were measured in isolated nuclei and RNA synthesis initiation sites were quantified in chromatin preparations. Stimulation of RNA polymerase I and II activities as well as an 85% increase in chromatin initiation sites were demonstrable within 1 h following DES treatment. Thus. these effects were closely correlated in time with increases in nuclear estrogen receptor levels and again preceded enhanced VLDL synthesis. Finally, a dose-related correlation was noted between accumulation of nuclear estrogen-receptor complexes and elevation of plasma triglycerides and VLDL following DES treatment. Collectively, these data provide evidence that estrogen receptor interaction may underwrite the physiologically important regulation of plasma lipoproteins by a mechanism involving both transcription and translation.